1. Field of the Invention
The present invention relates to an apparatus for detecting machining conditions in a machine tool during a machining process.
2. Description of the Prior Art
Prior art techniques for detecting machining conditions in a machine tool during a machining process include detection of machining strength, vibrations, sounds, heat, machining power, machining dimensions (residual stock removal quantity) or an exciting current (particularly if a spindle is supported by a magnetic bearing).
In accordance with the prior art, machining strength may be detected by use of a distortion gauge or a piezoelectric element mounted on a work rest or a tool rest. Alternatively a distortion gauge may be mounted on a work bearing center or variations, may be detected in pocket pressure of a static pressure fluid bearing which bears a tool (workpiece) spindle.
In accordance with the prior art, vibrations and sounds may be detected by use of an AE sensor or a vibration sensor provided on the work rest, the tool rest bearing center or a shoe. Alternatively, the AE sensor or the vibration sensor may be attached to the tool (workpiece) spindle for bearing a rolling bearing.
In accordance with the prior art heat may be detected by heat detection sensors embedded in the workpiece and the tool.
In accordance with the prior art, detection of the machining power involves a detection of the rotary driving power of the tool (workpiece) spindle.
In accordance with the prior art machining dimensions may be detected on the basis of a difference between a cutting feed per stroke and dimensions of the workpiece during the machining process.
In accordance with the prior art, exciting current in a magnetic bearing may be detected by detecting the average exciting current.
The following defects are inherent in the above mentioned prior art techniques for detecting the machining conditions.
The detection of machining strength is limited to a case where the workpiece is movable within a given range while restricting the rigidity of a workpiece support. Also, detection of machining strength limits a bearing mode of the workpiece to the center bearing, and decreases the response to variations in speed.
The detection of vibrations and sounds is applied only to a narrow range of abnormalities and involves the use of a bearing to thereby damp the vibrations, causing a drop in S/N ratio because rolling vibrations are also detected.
The detection of heat is of little practicability and has poor response as well.
The detection of machining power is, in addition to a poor response, limited to the power acting in a tangential line alone and is insufficient for a grinding process wherein variations in power acting in a normal line are large.
The detection of machining dimensions has low response because it is detected after effecting the machining process.
The exciting current cannot be detected in a frequency domain which allows detection of the exciting current to be averaged.
In any case, the prior art detection efficiency is low. In addition, the prior art only provides simple condition detecting means which is inadequate for analyzing multiple conditions by highly accurate detection and to output the output signal capable of effecting the corresponding control over the machine tool.